Many would think this would be a simple question to answer. Indeed most people would think that for a State like South Australia, with its strong tradition in natural history and scientific endeavour, we would know all of the species of plants and animals that exist within our boarders. Certainly there have been some tremendous milestones in our floral knowledge, for example, South Australia was the first State or Territory to have a flora (an inclusive description and identification tool for all plants, published by J.M Black in 1922), and the Census of South Australia (an up-to-date list of the State’s plants) is widely considered to be the best and most inclusive in Australia. This plant list currently puts the number of plant species in SA at around 5000.
However a comparison of the number of plants according to the plant list and the most recent edition of the flora, produced in the mid 1980s, indicates that over 1000 new species have been added over the last 20 years, that’s an average of 50 new species a year. With 73 new species recorded within the last year alone. So at least we can provide an approximate answer to the number of SA’s plant species, but why does the number change so rapidly over time? The answer to this lies at the interface of several scientific disciplines that are constantly being pushed beyond their boundaries by DEH staff and volunteers.
The first discipline is taxonomy, which aims to improve our imperfect knowledge of the natural boundaries between species. For example, some species may appear identical to the naked eye, except for a few microscopic features, but these few small differences indicate that in reality these species do not interbreed and maintain themselves as separate genetic units. As botanists get a clearer picture of the variation that exists across species, they are able to identify the morphological discontinuities that delimit them. In addition, field trips to remote locations in the state can often lead to the discovery of species that are new to science and have not been observed before. This discrimination and identification effort accounts for 34 of the 73 new species, and is largely due to the dedication of staff and volunteers at the State Herbarium.
We should also not rule out the possibility of discovery of batches of new species in the future. Indeed it is only within the last decade that literally hundreds of troglobytic (cave dwelling), stygofaunal (living in underground limestone aquifers) and mound spring invertebrate species have been discovered, and are still turning up at a rapid rate. However at the same time as discovering new species, four species have been struck off the SA plant list, because they were originally misidentified or no longer warrant recognition as a separate species due similarity with wider ranging species.
The second main area of activity providing new species knowledge are field surveys by the Biological Survey of South Australia, the regional ecologists and threatened species officers across the State. Overall 39 species that were originally known from outside SA, have been found by recent survey and field work within State boundaries. This total includes 3 species that were originally thought to have gone extinct (including an orchid, Thelymitra cyanapicata, and Viola species).Bringing these species back from the dead, is certainly a good news story, and many of these new findings are due to increased efforts to find species or surveys to areas not previously visited by qualified botanists.
However this second category of plants also hints at a worrying global trend, indicating an increasing rate of species turnover in our native plant communities. For example of the 39 species, previously known but recently found in SA, 15 (over 20%) are recorded as known weeds from elsewhere in Australia. It is also likely that a number of range expansions of both native and exotic species can be linked to recent trends in global warming, where in other parts of the world, there is evidence that species are starting to shift their ranges to escape harsh environments experienced in some parts of their historical distributions. Monitoring the changing distribution of the State’s natives and new influxes of invasive species will require intensive efforts in the near future. Such monitoring is the only way we will understand how and why species are changing in response to climatic and environmental shifts, and will allow us to develop planning and policy approaches to cope with the vagaries of this dynamic system.
Keeping on top of these changes has been a full time job, and now due to the large number of changes since the last state flora was published 20 years ago, a new flora project is underway. The new flora aims to provide an extensive update of the State’s floral taxonomic knowledge, and will provide an up-to-date and authoritative answer to the question, ‘how many plants do we have in SA’, at least for a short while anyway.
Article rewritten from that which appeared DEH Landscapes. Autumn 2008
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